Loeb, who is known for his activist investing via sharply worded letters kept a relatively low profile before his actions on Yahoo began. In the early 2000s, he was known for successfully shaking up companies like Agribrands (animal feed maker), Massey Energy (coal mining) and Star Gas Partners (fuel distributor), but had little to do with the technology sector.

Ironically, Loeb's interest in Yahoo this past year grew along with his own personal interest in technology, according to DealBook. He got an iPhone last year and grew fond of the Instagram app.

Last summer, Mr. Loeb was surprised to discover that someone had adopted his persona on Twitter under the handle "danloeb." Disappointed that the fake Mr. Loeb's postings were not witty, he reported the incident to Twitter, according to people close to him. The person switched the handle to "notdanloeb."